feature/skeleton-ballots

Builds out the skeleton app to match wireframes-v04, reshuffles preexisting NearbyPolling and FindElections views to their proper tabs, and loads the lists of contests in the root Ballot view.

Added docstrings for relevant methods using AppleDoc, a helpful primer is here: http://nshipster.com/documentation/

Also moved the Google Civic Info API key to its own plist file, and set its status to --assume-unchanged with git update-index.